Demons do the most damage
by SpnBloodStar
Summary: Jace and Clary head to check out a haunted house. But what happens when they find a demon waiting for them.
1. Chapter 1

**The mortal Instruments and it's characters belong to Cassandra Clare even though I would like a slice of Jace!**

**HEY! This is my first Mortal Instruments fic, but it just came to me so I sat down and wrote it. It's been on my laptop for a week but I didn't know whether to post it or not since it's not really a huge fan base. But my friend convinced me to post it anyway just in case. OK so here we go, enjoy... **

"So remind me why we are doing this again." Clary said staring at Jace.

"We are doing this, because I am bored and this place is supposed to be haunted!" Jace replied, smirking as he said it. They were standing in front of a large abandoned warehouse. Clary had seen this place, and went out of her way to never walk by it. It was dark and gave her the creeps, but she wasn't going to admit that to Jace. "You can hold my hand if you want." He taunted her. She batted his hand away and walked towards the building, planting a strong stare on her face. Jace followed with his hands in his pockets. He knew the place wasn't haunted but he really was bored and he thought it would be fun to scare Clary.

The door opened with a loud creak, "Well that's vaguely ominous," Jace announced. They walked in together and looked down the large hallway. They walked forward slowly, taking in the atmosphere. The first room they came to was missing a door and contained a desk, an office Clary presumed. This was the same for the room on the opposite side. The next room was bigger and full of boxes covered in dust.

The next was the biggest so far and was empty except for a small, dark pile in the corner. "Let's go in here." Jace said and pushed her in but stopped her a few feet in. The room was huge and Clary guessed it would have been where they actually made the products. Dust caked the flood but, looking over at the corner, didn't cover the pile. "Look," she said quietly to Jace, "No dust." Jace looked and then put his finger to his lips. 'Stay here' he mouthed and then walked silently over to the corner. Clary had to admire him; he didn't even kick up dust as he walked. She thought about how years of Shadowhunter training has that effect.

Jace stood right beside the pile now and bent slightly to look closer. It was then that the pile moved, a black sheet flew into the air and a man stood in front of Jace in a battle stance. The man had short brown hair and was wearing a tight shirt and jeans; she knew there was something wrong about him immediately. He smiled, showing a row of razor sharp teeth, it was then she realized he was a demon. Jace moved himself between Clary and the demon, chastising himself for not thinking to bring weapons. The demon moved first and dived for Jace, he missed and Jace jumped on him, straddling his waist. He landed a concession of punches on the demons face before he was punched hard in the jaw then thrown off and into the nearby wall. Jace sat there dazed with stars swimming in his vision. The demon stood and turned to face Clary. He walked long steps towards her then stop a few feet away.

The demon smirked at Clary, "You're pretty aren't you." He hissed seductively. He stalked closer to her, a stained knife raised in his hand. Clary tried to move, to run, but she was glued to the spot with fear. _This is it,_ she thought, _this is how I die! _

"MOVE!" Her head snapped round to see Jace running full pelt towards them, "CLARY, MOVE!" Her whole frame twitched and she began to move her feet but the demon was too close, the knife was going to drive right through her chest. She closed her eyes, waiting for the pain she knew would come, but she didn't feel it; instead she was tackled from the side by who she guessed was Jace.

The knife that was directed at Clary dug itself into Jace's shoulder. A scream escaped his lips as the strong blade fractured his shoulder blade, sending a burning sensation through his whole arm. They landed with a thud which made Clary gasp and sent more pain through Jace. He reached behind him and yanked the knife out of his wound, yelling through clenched teeth.

He pushed himself up with his other hand and turned to face the demon. "That really wasn't a good idea," He said, trying hard to plant his cocky smile on his face, but failing as it turned into a grimace.

"Oh did that hurt?" the demon said with false concern.

"Not as much as this will." He replied as he lunged toward the demon with the knife. The demon moved quickly away, laughing as he did so just to rub it in. Jace lunged again, this time missing on purpose to make the demon move; he quickly forced the demon into a corner. The demons face quickly turned from arrogance to horror, he knew what was about to happen, he had been stupid, laughing instead of paying attention. He had been cornered and Jace had his knife. He knew what he had to do, go down fighting, hurt Jace one more time before he perished. He leapt forward at the same time Jace did. The knife plunged into the demons chest and he felt himself begin to quake, he grabbed Jace's already injured shoulder and pulled on it. Hearing a glorious crack and the scream from Jace's lips made him smile as he crinkled inward on himself. The demon made a horrible sound as it burned and twisted itself. It soon became nothing but a small black burn on the floor, the only reminder of what had happened.

Jace turned to Clary who was sitting up, "You OK?" he asked quietly. She nodded slowly and stood up, "You?" she asked. He nodded in response but the grimace on his face betrayed him. She walked quickly towards him and got to him just as his knees buckled. She went down to her knees with him and held him upright, holding his head in the crook of her neck. She nervously moved her hand to Jace's shoulder and cringed at the wetness spreading down his back. She took her hand away and looked at the warm blood flowing over her hand and down her wrist; she pushed her hand back against it causing Jace to wince. "It's OK Jace," she said shakily, "I'll call Alec, just hold on OK." His hand moved slowly onto her leg, she took this as a response and reached inside her pocket for her phone.

He answered on the third ring. She told him what had happened and where they were then hung up and waited desperately for the sound of his car. She kept whispering to Jace and found comfort in his hand on her leg, which he would squeeze gently each time she spoke.

Ten minutes passed before she heard the screeching of tyres outside and she let out a breath, "They're here," she said, "Thank the angel, they're here." She pulled her head back and looked at Jace's face, all the colour was gone, and his eyes were barely open. She'd never seen him like this and it scared her to the core. She stroked his face and his hair out of his eyes, and then pulled him back to her. Footsteps pounded down the hallway getting louder and voices yelled out to Clary.

"In here," she responded, "We're in here!" She let out a sigh of relief as Alec ran though the open door followed by Isabelle. Alec dropped to his knees behind Jace. "Iz, you take over from Clary."

"No I got him," Clary said, not wanting to let go.

"Clary," Alec looked at her desperately.

"I got him; just do what you need to do." Alec nodded to Isabelle who knelt beside her just in case and then proceeded to rip the shirt off Jace's back. He tried to mop up the blood with the scraps but the shirt was already soaked. He took off his jacket and held that against the wound. He then wiped away a patch of blood and pulled out his stele. He took a deep breath to steady his hand and then carefully drew an Iratze onto Jace's back.

"Wait, it won't work, it's a demon knife." Isabelle said staring at the knife a few feet away.

"We have to try." Alec responded, desperation in his voice. "OK Clary I'm gonna pick him up so just move him towards me," Clary carefully pushed Jace into Alec's waiting arms, and then pushed herself to her feet. She looked down and saw a small pool of blood on the floor, she realised how much Jace must be bleeding.

Alec carefully lifted Jace to his feet putting his arm around Jace's waist. Isabelle took the other side, holding the jacket over his wound and they carefully dragged him out of the building and sat him in the back of the car. Alec drove with Isabelle in the seat next to him. Clary sat beside Jace with a hand on his chest making sure he stayed leaned back against the chair to hold the jacket in place against his shoulder.

In just under ten minutes they were at the institute and Alec had swept Jace up his arms saying it would take too long to walk him to the infirmary. They waited impatiently as the elevator creaked down. When the doors opened Alec ran ahead and pushed through the infirmary doors. Clary went to step through but Isabelle stopped her, putting a hand on her arm, "Let us work, you won't want to see this." She backed though the door and then shut it in front of Clary.

Clary stood outside the room for a few minutes then noticed her bloodied hands. She reluctantly went to her room to shower and change as her clothes were also stained with blood.

She pushed through her door, and closed it behind her. She walked to her draws, took out a towel, then went through to the bathroom and switched on the shower. Kicking off her shoes, she caught a glimpse of herself in the mirror. He face was streaked with dust and dried tears she hadn't even know she'd shed, and there were lines of blood around her face. Suddenly the night's events rushed back to her and she had to sit down. She sat on the toilet and lowered her head into her hands. Tears began to flow down her face and she sobbed freely.

**OK so I thought this would be a good place to stop. There is more to come and I have pretty much finished the next chapter but if I get no reviews I won't bother posting it. OK so thanks to anyone that actually read this. Taryn X**


	2. Chapter 2

**OK so I got the reviews I wanted so here's the next chapter. I guess I should explain that they still believe they are related in the story so just to put that straight. OK so let's continue...**

An hour later she was lying on her bed after pulling herself together to shower and change. She hadn't heard anything about Jace, and it was tearing her apart. She couldn't wait anymore for information. She pushed herself off the bed and walked out the door. She walked quickly towards the infirmary. She wouldn't be sent away this time; she had a right to know what was going on. After all Jace was her brother and he had jumped in front of the knife to protect her. She braced herself for what was to come then pushed through the infirmary doors.

The stench of antiseptic ambushed her nose as she located Jace with her eyes. He was in the bed furthest from the door and Alec was standing over him with his back to her. She walked towards him but stopped abruptly when Alec turned to face her.

"Clary," He said in warning, "You shouldn't be here."

"Why not? I have every right to be here." She said, annoyed that Alec was treating her like a child.

"I...I guess you do, but it's not something you should see."

"What's wrong?" She asked timidly. Alec bowed his head slightly then put his hand on her arm.

"Normally we could just stitch up the wound and the only issue would be his blood loss, but it's different this time. The Iratze is healing his broken shoulder blade and we stitched him up and replenished his blood but there another problem. When he was stabbed there must have been d..." Alec stopped briefly to take a deep breath, "There must have been demon blood on the knife and it has entered his blood stream. It's hurting him Clary, and unless we get it out, it will kill him." Clary stood in shock. Demon blood? She had saw the stains on the knife and thought nothing of it, admittedly because it was heading right for her chest at the time, but she didn't even know demon blood could do this. She hid her eyes for a moment as tears threatened to fall, then looked up at Alec.

"I want to see him." She said with a quiver in her voice. "Please Alec."

He nodded but said, "Just prepare yourself. It... Well just look." He moved aside so Clary could see. She stepped forward slowly and saw Jace laying on his stomach his head facing away from her. Alec turned and lifted the blanket that was covering Jace's wound and moved it down to his waist. Clary gasped. She didn't know what to expect but in no way could she have imagined this. Thin black lines snaked away from the stab wound on Jace's shoulder, stopping about two inches out at every angle.

"Is that...?" She begun to ask, but couldn't bring herself to say the words.

"The demon blood. It's tainting Jace's blood. It's affecting his cells and in turn, affecting his veins and arteries. See how it's turning them black? It's slowly contaminating them. He'll be OK, well kind of OK, until these lines reach his chest. Once they reach his heart he'll..." He stopped seeing how upset Clary was and couldn't finish that sentence. Saying that he'll die would destroy her. Not just her but him too, his whole family would hate to lose Jace. He was a member of their family, always would be. He put his arm around Clary and slowly pulled her into a hug. He rested his chin on her head and said softly, "We won't let that happen. We won't let it get that close."

The door opened and Isabelle walked in, her eyes red and puffy. She saw Alec and Clary and dashed over to them.

"Oh Clary." Was all she said as she took her off Alec and hugged her tightly. A few more tears fell from her eyes into Clary's hair. "Clary, it's gonna be OK," She said softly into Clary's ear, "We'll stop it, get it out. He'll be back to his normal self soon enough." She pulled away and looked into Clary's eyes. "OK?" She said. Clary nodded in response.

Clary wiped her eyes on her sleeves then turned back to Jace. Alec had covered his shoulder back up, and for this she was grateful. She walked around the other side of the bed and looked at Jace's face. His face was white as a sheet and was covered with a sheen of sweat. She pulled a chair around the bed and sat down beside him. She put her elbows on her knees and stared at Jace.

This was her fault, she thought. If only she had run, if only she had moved, Jace wouldn't have had to protect her, and he wouldn't have been stabbed. She remembered clearly the noise he made when the knife pierced his shoulder, the scream that he let out. She had never heard Jace make a noise like that before; she had never heard anyone make a noise like that before. She had watched him stand off against that demon with blood pouring down his back; even injured like that he was able to fight like a pro. Then, when Jace leapt at the demon, when she thought it was all over, she heard that crack. That horrible, gut wrenching crack, followed by the scream she never wants to hear again. Jace may have won then, but he was losing now. She looked at his face and saw his eyes moving under his lids. She wondered what he was dreaming about. Whether it was a good or bad dream. Whether it was about the demon or about her. She was glad that he was asleep though, he shouldn't have to be awake through the pain that Clary was sure was there. At least for now he could sleep, dream maybe. Clary then realised how tired she was and closed her eyes. A little nap couldn't hurt and she knew that someone would wake her up if Jace woke up. She thought once more about that horrible crack and the scream that followed before drifting into sleep.

**So what do you think? Reviews make me happy so don't let me be sad please! I hope you are enjoying the story and I'm gonna start writing the next chapter after uploading this. OK thanks to everyone that has read so far! Oh and just remembered. It may not be mentioned in the book whether demon blood does this(I can't remember and I've lost my copy of the book lol), but it's an idea that came to me and I really liked it so I thought I'd write it to see if it worked and if people liked it. If you don't like the idea of what the demon blood does, let me know! OK so thanks! Taryn x**


	3. Chapter 3

**OK so I got the reviews I wanted so here's the next chapter. I guess I should explain that they still believe they are related in the story so just to put that straight. OK so let's continue...**

An hour later she was lying on her bed after pulling herself together to shower and change. She hadn't heard anything about Jace, and it was tearing her apart. She couldn't wait anymore for information. She pushed herself off the bed and walked out the door. She walked quickly towards the infirmary. She wouldn't be sent away this time; she had a right to know what was going on. After all Jace was her brother and he had jumped in front of the knife to protect her. She braced herself for what was to come then pushed through the infirmary doors.

The stench of antiseptic ambushed her nose as she located Jace with her eyes. He was in the bed furthest from the door and Alec was standing over him with his back to her. She walked towards him but stopped abruptly when Alec turned to face her.

"Clary," He said in warning, "You shouldn't be here."

"Why not? I have every right to be here." She said, annoyed that Alec was treating her like a child.

"I...I guess you do, but it's not something you should see."

"What's wrong?" She asked timidly. Alec bowed his head slightly then put his hand on her arm.

"Normally we could just stitch up the wound and the only issue would be his blood loss, but it's different this time. The Iratze is healing his broken shoulder blade and we stitched him up and replenished his blood but there another problem. When he was stabbed there must have been d..." Alec stopped briefly to take a deep breath, "There must have been demon blood on the knife and it has entered his blood stream. It's hurting him Clary, and unless we get it out, it will kill him." Clary stood in shock. Demon blood? She had saw the stains on the knife and thought nothing of it, admittedly because it was heading right for her chest at the time, but she didn't even know demon blood could do this. She hid her eyes for a moment as tears threatened to fall, then looked up at Alec.

"I want to see him." She said with a quiver in her voice. "Please Alec."

He nodded but said, "Just prepare yourself. It... Well just look." He moved aside so Clary could see. She stepped forward slowly and saw Jace laying on his stomach his head facing away from her. Alec turned and lifted the blanket that was covering Jace's wound and moved it down to his waist. Clary gasped. She didn't know what to expect but in no way could she have imagined this. Thin black lines snaked away from the stab wound on Jace's shoulder, stopping about two inches out at every angle.

"Is that...?" She begun to ask, but couldn't bring herself to say the words.

"The demon blood. It's tainting Jace's blood. It's affecting his cells and in turn, affecting his veins and arteries. See how it's turning them black? It's slowly contaminating them. He'll be OK, well kind of OK, until these lines reach his chest. Once they reach his heart he'll..." He stopped seeing how upset Clary was and couldn't finish that sentence. Saying that he'll die would destroy her. Not just her but him too, his whole family would hate to lose Jace. He was a member of their family, always would be. He put his arm around Clary and slowly pulled her into a hug. He rested his chin on her head and said softly, "We won't let that happen. We won't let it get that close."

The door opened and Isabelle walked in, her eyes red and puffy. She saw Alec and Clary and dashed over to them.

"Oh Clary." Was all she said as she took her off Alec and hugged her tightly. A few more tears fell from her eyes into Clary's hair. "Clary, it's gonna be OK," She said softly into Clary's ear, "We'll stop it, get it out. He'll be back to his normal self soon enough." She pulled away and looked into Clary's eyes. "OK?" She said. Clary nodded in response.

Clary wiped her eyes on her sleeves then turned back to Jace. Alec had covered his shoulder back up, and for this she was grateful. She walked around the other side of the bed and looked at Jace's face. His face was white as a sheet and was covered with a sheen of sweat. She pulled a chair around the bed and sat down beside him. She put her elbows on her knees and stared at Jace.

This was her fault, she thought. If only she had run, if only she had moved, Jace wouldn't have had to protect her, and he wouldn't have been stabbed. She remembered clearly the noise he made when the knife pierced his shoulder, the scream that he let out. She had never heard Jace make a noise like that before; she had never heard anyone make a noise like that before. She had watched him stand off against that demon with blood pouring down his back; even injured like that he was able to fight like a pro. Then, when Jace leapt at the demon, when she thought it was all over, she heard that crack. That horrible, gut wrenching crack, followed by the scream she never wants to hear again. Jace may have won then, but he was losing now. She looked at his face and saw his eyes moving under his lids. She wondered what he was dreaming about. Whether it was a good or bad dream. Whether it was about the demon or about her. She was glad that he was asleep though, he shouldn't have to be awake through the pain that Clary was sure was there. At least for now he could sleep, dream maybe. Clary then realised how tired she was and closed her eyes. A little nap couldn't hurt and she knew that someone would wake her up if Jace woke up. She thought once more about that horrible crack and the scream that followed before drifting into sleep.

**So what do you think? Reviews make me happy so don't let me be sad please! I hope you are enjoying the story and I'm gonna start writing the next chapter after uploading this. OK thanks to everyone that has read so far! Oh and just remembered. It may not be mentioned in the book whether demon blood does this(I can't remember and I've lost my copy of the book lol), but it's an idea that came to me and I really liked it so I thought I'd write it to see if it worked and if people liked it. If you don't like the idea of what the demon blood does, let me know! OK so thanks! Taryn x**


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